A double container having a flexible outer container and an inner bag containing the contents with a space between the outer container and the inner bag is capable of retaining the shape of the outer container even when the inner bag is deformed with a decrease of its volume according as the contents are consumed.
In case where the contents of such a double container comprise a component which decomposes to generate gas, there is a fear that the decomposition gas expands and bursts the container during storage. It is therefore necessary to make a ventilation passage interconnecting the inside of the container to the open air so as to let out the decomposition gas. Further, it is desirable that the space of the container be ventilated through a ventilation passage during storage.
On use of the double container, on the other hand, it is necessary to shut the ventilation passage to keep in air or gas of the space so that a pressing force imposed to the outer container may be transmitted to the inner bag, whereby the contents can be discharged from the tip of the cap fitted on the container.